Optical interconnects are replacing electrical interconnect because of their higher data transfer rate and reduced power consumption. To recover transmitted data, optical transceivers include a CDR circuit whose function is to extract and retime the incoming data at an appropriate phase. The CDR circuit ensures that the original data, which becomes distorted while passing through an electrical channel, is recovered error free. To extract the original data, a reference clock is either supplied to the CDR circuit from an external circuit or is extracted from the data itself by the CDR circuit (i.e., a reference-less CDR circuit). In many electrical applications such as a chip-to-chip or board-to-board transceiver, a local clock is readily available to the CDR circuit. However, in compact optical modules, space and power constraints may mean a reference clock is not available, and thus, a reference-less CDR circuit must be used.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.